Field of the Invention
The present invention relates to a common rail system for an internal combustion engine of a vehicle.
Background of the Invention
Common rail systems as fuel injection systems are known in prior art, which comprise a high-pressure pump for providing high-pressurized fuel for a high-pressure accumulator (common rail) and a low-pressure pump as a preliminary conveyance pump, which conveys the fuel from a fuel tank via a conveyor line to the high-pressure pump, with the quantity of fuel conveyed by the high-pressure pump to the high-pressure accumulator being controlled by a flow control valve arranged in the conveyor line and the quantity of fuel measured by the flow control valve being impinged by the high-pressure pump with the respectively high pressure.
Such a common rail system CRS is schematically shown in FIG. 4. Accordingly, this common rail system CRS comprises a high-pressure accumulator R, from which injection valves Inj of an internal combustion engine (not shown), for example a diesel engine, are being supplied with fuel.
The high-pressure accumulator R is connected via a high-pressure line L1 to a high-pressure pump HP, which is driven by an electric motor M1. From a fuel tank KB, via a low-pressure pump NP driven by an electric motor M2, fuel is conveyed via a conveyor line L2 to a flow control valve VNC, which is embodied as an electromagnetic switching valve showing the design of a slide valve and which in the un-electrified state is closed (“normally closed”). At the outlet side this slide valve VNC is connected to the high-pressure pump HP.
Finally, a high-pressure control valve HPV connects the high-pressure accumulator R via a pressure release line L3 to the outlet side of the low-pressure pump NP. This high-pressure control valve HPV, embodied as an electromagnetic switching valve, serves for the rapid pressure reduction of the high-pressure accumulator R.
This high-pressure control valve HPV is required here because advantageously the slide valve VNC does not show 100% freedom from leakage. This leakage is caused in the play between this slide element and the valve body required to displace the sliding element. This leads to the circumstance that during the sliding operation fuel enters the high-pressure pump HP and is compressed there, resulting in the pressure increasing in the high-pressure accumulator R if the injectors Inj provide no fuel to the internal combustion engine, thus no consumer is connected to the high-pressure accumulator R. In such operating states the pressure is released via the high-pressure control valve HPV.
Here the flow control valve VNC, the high-pressure and the low-pressure pump HP and NP, respectively, the high-pressure control valve HPV, as well as the injection valves Inj are controlled and/or adjusted by a control device (not shown).
A common rail system according to FIG. 4 is known for example from DE 60 2005 003 427 T2, in which a slide valve is used as the flow control valve, which is closed in the un-electrified state. In order to counteract the disadvantages developing by the use of common slide valves, in addition to the lack of
freedom from leakage, namely insufficient centering of the slide element in the valve chamber and the thereby caused lack of ability to glide, which leads to increased wear and tear by high abrasion, an improved design of a slide valve is suggested. This improved design relates to the embodiment of the slide element.
The disadvantage of insufficient freedom from leakage when using a slide valve in a common rail system is eliminated according to DE 198 46 157 A1 such that at the outlet side of the flow control valve both a reflux line is provided leading back to the fuel tank as well as a differential pressure valve is connected here, which is connected to the suction valves of a high-pressure pump. This way it is achieved that the high-pressure pump in the operating state “zero conveyance” abstains from conveying any fuel, because the differential pressure valve cannot be overcome by the leakage flow of the flow control valve.
Another disadvantage of the use of the “normally closed” slide valve in common rail systems is given in the fact that in case of a defect or the failure of such a slide valve no fuel can be conveyed into the rail, thus into the high-pressure accumulator, and thus any further operation of the internal combustion engine is impossible.
The invention is based on the objective to further develop the underlying common rail system according to the type mentioned at the outset such that the disadvantages known from prior art are avoided, particularly a simple design is possible with only few parts.